Timing control valve in automatic transmission control apparatus

ABSTRACT

A timing control valve for use in the automatic transmission control apparatus for vehicles has a spring-backed spool which is actuated for movement to one position by the spring force or the spring force and the oil pressure to be applied to the brake B 2  for causing a sun gear and a transmission gear case to be engaged by way of a one-way clutch, and is actuated for movement to the other side by a counteracting force provided by a line pressure and an oil pressure to be applied to the reverse clutch C 2 , whereby the timing control valve permits the brake B 1  to be operated for directly connecting or disconnecting the sun gear and transmission case by controlling the timing of such operation of the brake B 1  in response to changes in the throttle opening degree, and particularly permit a smooth downshifting without a one-way clutch.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a timing control valve for use in theautomatic transmission control apparatus for vehicles, which is providedin the hydraulic control circuit for controlling the operation timing ofbrakes, clutches, etc. in the transmission unit so that they can beoperated at appropriate timings at each shifting.

2. Description of the Prior Art

When a shifting from a higher speed gear ratio to a lower speed gearratio (downshifting) takes place, brakes, clutches or one-way clutch onthe one hand, which are being engaged in a higher speed gear ratio("shift range" or "speed" hereinafter) and are to be disengaged orreleased in a lower speed shift range, and brakes, clutches or one-wayclutch on the other hand, which are being released in the higher speedshift range and are to be engaged in the lower speed shift range areengaged and or released at appropriate timings. However, in order topermit a smooth downshifting, intervals or timing lags between thosetimings should desirably tend properly to increase with an increasingengine speed or with increase in throttle opening degree which is incorrelation with the engine speed. It has been known that to properlyincrease those timing lags is particularly important in clutch-to-clutchdownshifting without the aid of an intermediate one-way clutch.

A conventional timing valve as shown in FIG. 1 which provides timing lagcontrol functions as described above. The timing valve shown in FIG. 1is actuated by a spring 52 backing one side of the spool 51, and by athereagainst counteracting operating oil pressure PC₂ from a hydraulicservo unit applied on a piston portion 53 of the spool 51. The pressurePC₂ causes the clutch C₂ to be engaged in a higher speed shift range andto be disengaged in a lower speed shift range, so that the timing valvecontrols oil pressure supply to the brake B₁ permitting the brake B₁ tobe engaged after a certain timing lag or delay when a downshifting tothe lower speed shift range takes place. As the operating hydraulic(oil) pressure PC₂, which is proportional to a line pressure PLintroduced into a hydraulic circuit through a pressure regulating valvefor regulating an output pressure of an oil pump driven by the engine,rises in accordance with increase in the engine speed or throttleopening degree, the operating oil pressure PC₂ which lies at an elevatedstate will take a longer time before being wholly exhausted, thusallowing an increased timing lag between releasing step of the clutch C₂and subsequent engaging step of the brake B₁. However, according to theconventional timing valve, it is impossible to provide a sufficienttiming lag change to meet the required timing lag corresponding to theincrease in the throttle opening degree.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a timing valvefor use in the automatic transmission control apparatus permittingproper increase in the timing lag at which the clutches, brakes andother elements can be operated on shifting to a lower speed shift range,in response to increase in the throttle opening degree, etc., andtherefore permitting a smooth downshifting.

The invention includes a timing control valve for use in an automatictransmission control apparatus of a type in which a shifting to oneshift range is effectuated essentially by engaging a brake B₁ foroperating engine brake or aiding in operating of a one-way clutch, andby engaging a clutch C₁. The timing control valve functions in such amanner that a shifting from a higher speed shift range to said one shiftrange is effectuated by causing the brake B₁ to be engaged afterreleasing a clutch C₂ which has been in engagement at the higher speedshift range and causing the one-way clutch to be engaged if this isprovided. The present invention provides a timing control valve which asessential elements comprises a spool backed with a spring on one sidethereof, and a hydraulic line pressure medium and a hydraulic servopressure medium to be applied to a clutch C₂ which are exerted onrespective piston portions of the spool with each specifiedpressure-applicable area counteracting against the spring force. Thespool is thereby actuated to control, i.e., to supply or release ahydraulic pressure which is applied to the brake B₁.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a conventional timing control valvearrangement;

FIG. 2 is a schematic view of a timing control valve arrangementaccording to the present invention;

FIG. 3 is a diagram of a hydraulic circuit incorporating the timingcontrol valve according to the present invention;

FIG. 4 is a schematic diagram of an automatic transmission controlled bythe hydraulic circuit of FIG. 3;

FIG. 5 is a graphical representation of variations in the operating oilpressure PC₂ required for shifting from the third to second speedshifting range; and

FIG. 6 is a block diagram of the electrical circuit for controllingsolenoid valves as shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One preferred embodiment of the present invention is now described inmore detail with reference to from FIG. 2 to FIG. 6.

FIG. 2 shows an embodiment of the timing control valve according to theinvention, generally shown by 340, the arrangement comprising on theright side a fluid ("oil" hereinafter) chamber 341 in which a linepressure PL is introduced and a piston portion ("land" hereinafter) 342of a pressure-applicable area A₁ whereon the line pressure PL is to beapplied; and on the left side an oil chamber 344 which is communicatedto an inner piston I of a clutch C₂ which in this embodiment is engagedin the third speed shift range ("speed" hereinafter) and is to bereleased in the second speed and a land 342 of a greater applicable areaA₂ than that of the land 343 to which the operating oil pressure PC₂ isto be applied for operating the inner piston I. The valve arrangement340 further has an oil chamber 346 communicated to the brake B₂ whichoperates the one-way clutch F₁ so arranged in this embodiment, as to beoperated in the second speed; a spool 347 arranged in a oil chamber 346as well as defining said oil chamber and having the land 346' to whichthe operating oil pressure PB₂ for the brake B₂ is applied; a spring 345biasing the spool 347 by exerting a resilience force Fs, an oil chamber348 from which an oil pressure is supplied to the brake B₁ foreffectuating an engine brake according to the movement of the spool 347in the second speed when the manual shift valve is placed in a D rangeand a 2 range; and an oil chamber 349 from which oil pressure issupplied to the outer piston O which cooperates with the inner piston Ito actuate the clutch C₂ into its engagement when, in this embodiment, ashifting to reverse is effected.

The operation of the above described timing control valve will bedescribed.

FIG. 3 is a diagram of an example of the hydraulic circuit in theautomatic transmission control apparatus, in which the timing controlvalve is provided, the hydraulic circuit operating a hydrodynamicautomatic transmission including an overdrive unit as shown in FIG. 4.The automatic transmission includes a torque converter 1 with adirect-coupling clutch 50, an overdrive unit 2 and a transmission gearunit 3 which provides three forward speeds and one reverse. The torqueconverter 1, which is known per se, comprises a pump 5, a turbine 6 anda stator 7, the pump 5 being connected to an engine crankshaft 8, andthe turbine 6 being connected to a turbine shaft 9. The turbine shaft 9provides an output shaft for the torque converter 1 and also provides aninput shaft for the overdrive unit 2. The turbine shaft 9 is connectedto a carrier 10 of a planetary gear set for the overdrive unit 2. Thedirect-coupling clutch 50 is interposed between the engine crankshaft 8and turbine shaft 9, and is actuated to mechanically connecting thecrankshaft 8 with the turbine shaft 9. A planetary pinion (or a set ofpinions) 14 rotatably supported by the carrier 10 engages a sun gear 11and a ring gear 15. An overdrive multi-disc clutch C₀ and an overdriveone-way clutch F₀ are interposed between the sun gear 11 and the carrier10, and an overdrive multi-disc brake B₀ is interposed between the sungear 11 and a housing or overdrive casing 16 which accommodates theoverdrive unit.

The ring gear 15 in the overdrive unit is connected to an input shaft 23of the transmission gear unit 3. A front multi-disc clutch C₁ isprovided between the input shaft 23 and shaft 29, with a reversemulti-plate clutch C₂ disposed between the input shaft 23 and sun gearshaft 30. A multi-disc brake B₁ and a multi-disc brake B₂ which isoperable through a one-way clutch F₁ are provided between the sun gearshaft 30 and transmission case 18. A sun gear 32 fixed on the sun gearshaft 30 forms a planetary gear train composed of two planetary gearsets, one set including a carrier 33, a planetary pinion 34 carried bythe carrier 33 and a ring gear 35 in mesh with the pinion 34, and theother set including a carrier 36, a planetary pinion 37 carried by thecarrier 36 and a ring gear 38 in mesh with the pinion. The ring gear 35in one of the planetary gear sets is connected to the shaft 29. Thecarrier 33 in this gear set is linked to the ring gear 38 in the othergear set, the carrier 33 and the ring gear 38 being connected to theoutput shaft 39. A multi-disc brake B₃ and a one-way clutch F₂ areprovided between the carrier 36 in the other gear set and thetransmission case 18.

The hydrodynamic automatic transmission hereinabove described iscontrolled by the hydraulic control circuit which will later bedescribed wherein each clutch and brake can be engaged or disengagedaccording to the engine output changes and cruising speeds of theautomobile, thus providing the corresponding shift ranges (or speeds) offour forward speeds including an overdrive speed (O/D) or a manuallyswitched shifting to a reverse gear.

Transmission gear positions and brake operations are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________           Friction engagement elements                                                                              one-                                                                              one-                                                                              one-                                                                  way way way                                Shift  clutch                                                                            clutch                                                                            clutch                                                                            brake                                                                             brake                                                                             brake                                                                             brake                                                                             clutch                                                                            clutch                                                                            clutch                             positions                                                                            C.sub.0                                                                           C.sub.1                                                                           C.sub.2                                                                           B.sub.0                                                                           B.sub.1                                                                           B.sub.3                                                                           B.sub.2                                                                           F.sub.0                                                                           F.sub.2                                                                           F.sub.1                            __________________________________________________________________________    Parking (P)                                                                          O   X   X   X   X   O   X                                              Reverse (R)                                                                          O   X   O   X   X   O   X   lock                                                                              lock                                   Neutral (N)                                                                          O   X   X   X   X   X   X                                              Forward                                                                       D range                                                                       1st    O   O   X   X   X   X   X   lock                                                                              lock                                                                              over-                                                                         run                                2nd    O   O   X   X   O   X   O   lock                                                                              over-                                                                             lock                                                                      run                                    3rd    O   O   O   X   X   X   O   lock                                                                              over-                                                                             over-                                                                     run run                                O.D    X   O   O   O   X   X   O   over-                                                                             over-                                                                             over-                                                                 run run run                                3 range                                                                       1st    O   O   X   X   X   X   X   lock                                                                              lock                                                                              over-                                                                         run                                2nd    O   O   X   X   X   X   O   lock                                                                              over-                                                                             lock                                                                      run                                    3rd    O   O   O   X   X   X   O   lock                                                                              over-                                                                             over-                                                                     run run                                2 range                                                                       1st    O   O   X   X   X   X   X   lock                                                                              lock                                                                              over-                                                                         run                                2nd    O   O   X   X   O   X   O   lock                                                                              over-                                                                             lock                                                                      run                                    L range                                                                              O   O   X   X   X   O   X   lock                                                                              lock                                                                              over-                                                                         run                                __________________________________________________________________________

In the above table, a symbol "O" indicates that the appropriate clutchor brake is engaged, and a symbol "X" indicates that the appropriateclutch or brake is disengaged.

FIG. 3 illustrates a preferred embodiment of the fluid circuit in thehydraulic control apparatus according to the present invention, whichpermits an automatic or manual shifting of gears by selectivelyoperating the clutches C₀, C₁, C₂ and brakes B₀, B₁, B₂, B₃ of theautomatic transmission, and the direct-coupling clutch 50 of the torqueconverter. In FIG. 3, the fluid circuit comprises an oil tank 100, anoil pump 101, a pressure regulating valve 102, an auxiliary pressureregulating valve 103, a cutback valve 190, a throttle valve 200, amanual valve 210, a 1-2 shift valve 220, a 2-3 shift valve 230, a 3-4shift valve 240, a low coast modulator valve 250, an intermediate coastmodulator valve 255, accumulator valves 260, 270, 280, checkvalve-incorporated flow control valves 290, 300, 305, 310, solenoidvalve 320, 330, a timing valve according to the present invention 340, acooler bypass valve 350, a direct coupling clutch control valve 360, adirect coupling control solenoid valve 370, oil passages between theabove-mentioned valves and passages for supplying pressure oil to fluidservo elements of the clutches and brakes from the valves.

Operating oil which is drawn by the oil pump 101 from the oil tank 100is introduced into the pressure regulating valve 102, which regulatesoil to a predetermined pressure (line pressure), the regulated oil beingbranched into an oil pasaage 104 and an oil passage 103'. The oilthrough the passage 103' is introduced into the auxiliary pressureregulating valve 103 providing torque converter pressure, lubricatingpressure and cooler pressure which are regulated to predetermined valuesdepending on throttle pressures of the throttle valve 200. The manualvalve 210 connected to the oil passage 104 is operatively associatedwith a shift lever located at a driver seat. Manually operating theshift lever brings the manual valve 210 to positions P, R, N, D, 3, 2and L depending on the range positions in the shift lever. Table 2summarizes the relationships between oil passage 104 and oil passages105, 106, 109, 110 at each of the shift lever positions, the symbol "O"meaning that the oil passage communicates with the appropriate oilpassages.

                  TABLE 2                                                         ______________________________________                                                P      R     N       D   3     2   L                                  ______________________________________                                        oil passage 105          O     O   O     O   O                                oil passage 106                O   O     O   O                                oil passage 109                              O                                oil passage 110    O                                                          ______________________________________                                    

The first solenoid valve 320 controlling the 2-3 shift valve 230 has itsport 321 closed when it is not energized, causing oil to be pressurizedin an oil passage 111 communicated with the oil passage 106 through anorifice 322. Energizing the valve 320 causes its port 321 to open,allowing the pressurized oil in the passage 111 to be drained through adrain port 323. The second solenoid valve 330 which controls the 1-2shift valve 220 and 3-4 shift valve 240 has its port 331 closed when itis not energized, causing oil to be pressurized in an oil passage 112communicated with the oil passage 104 through an orifice 332. Energizingthe solenoid valve 330 causes its port 331 to open, allowing thepressurized oil in the passage 112 to be drained from a drain port 333.Table 3 shows the relationships between the solenoid status of thesolenoid valves 320 and 330 which are energized or disenergized undercontrol of an electronics circuit later to be described, and thecorresponding shifting to four speeds and neutral in the automatictransmission.

                  TABLE 3                                                         ______________________________________                                        Manual valve     D range                                                      shift position       1st     2nd   3rd   4th                                  Gear shift range                                                                          N range  speed   speed speed speed                                ______________________________________                                        1st solenoid valve                                                                        OFF      ON      ON    OFF   OFF                                  2nd solenoid valve                                                                        OFF      ON      OFF   OFF   ON                                   ______________________________________                                    

The 1-2 shift valve 220 has a spool 222 backed with a spring 221, andsince in the first speed of the gear shift range the solenoid valve 330is being energized allowing oil pressure to be released from the oilpassage 112, the spool 222 is set to the right position in the figuredue to the oil pressure supplied through an oil passage 113 to an oilchamber 223 at the left end. In the second speed, the solenoid valve 330is disenergized, providing the oil pressure in the oil passage 112,which sets the spool 222 to the left position in the figure. In thethird and fourth speeds, the spool 232 in the 2-3 shift valve 230, whichwill be described later, is set to the right position in the figure,causing the oil pressure to be released from the left end oil chamberthrough the oil passage 113, which results in setting the spool 222 tothe left position.

The 2-3 shift valve 230 has a spool 232 backed by a spring 231. In firstand second speeds, the solenoid valve 320 is energized with no oilpressure in the oil passage 111, causing the spring 231 to move thespool 232 to the left position. In the third and fourth speeds, thesolenoid valve 320 is disenergized, producing oil pressure in thepassage 111, which sets the spool 232 to the right position.

The 3-4 shift valve 240 has a spool 242 backed by a spring 241 on oneside thereof, and in first and second speeds, a line pressure is drawninto an oil chamber 243 through an oil passage 114, setting the spool242 to the left position. In the third and fourth speeds, the oilpressure is released from the oil pressure 114; in the third speed, thesolenoid valve 330 is energized allowing the passage 112 to be releasedwith the pressure, and causing the spring 241 to urge the spool 242toward the left setting position; and in the fourth speed, the solenoidvalve 330 is disenergized producing the oil pressure in the passage 112,setting the spool 242 to the right position in the figure.

The throttle valve 200 is actuated in response to the stroke of theaccelerator pedal depressed, causing a corresponding stroke in anindicator valve 201, which in turn compresses a spring 203 interposedbetween the indicator valve 201 and a valve spool 202, producing athrottle pressure in an oil passage 124.

With the manual valve 210 at N position, the solenoid valve 330 isdisenergized and there is oil pressure in the oil passage 112,introducing oil pressure into left-end oil chamber 224 of the 3-4 shiftvalve 240 whose spool 242 is set to the right position. In this state,the 3-4 shift valve 240 allows a communication between oil passages 104and 115, and the brake B₀ is engaged; the oil passage 120 iscommunicated to the drain port 245 from which the oil pressure isreleased, and the clutch C₀ is released; thus the overdrive unit 3 iswith its overdrive gears in mesh.

Manually shifting the manual valve 210 to R position produces oilpressure in the oil passage 110, introducing the oil pressure into theright oil chamber 243 of the 3-4 shift valve 240 by way of the 2-3 shiftvalve 230 with its spool 232 set to the left position and through theoil passage 114. Thus, when the manual valve 210 is changed from N- to Rposition, the overdrive gears in the overdrive unit 2 are kept in meshfor about one second, and the reverse gears in the change (planetary)gear train 3 come to engagement. One second after the shifting from N toR, the oil chamber 243 receives a rising oil pressure, moving the spool242 to the left position to allow the oil pressure 104 to communicatewith the oil passage 120 which introduces the oil pressure to the clutchC₀ simultaneously releasing oil pressure from the oil passage 115, sothat the brake B₀ is released and the clutch C₀ is engaged. The gears inthe overdrive unit 2 are thus in a direct-coupled condition, and theplanetary gear train is thus brought to a normal reverse gearing.

In case where the multi-disc clutch C₂ for reverse which is arranged inthe change gear train 3 of the automatic transmission is provided withan inner piston I and an outer piston O as a hydraulic servo unit, it isnecessary to produce a timing lag (or timing interval) betweenoperations of both pistons in order to secure smooth gear engagement atreverse. Therefore, a passage 126 branched from the passage 110 isprovided which is communicated via the timing valve 340 to the passage127 which leads to the outer piston O of the clutch C₂. In thisarrangement, the timing valve 340 with its spool 347 set at the leftside actuates the outer piston O by communicating the passage 126 withthe passage 127, whereas with its spool 347 set at the right side thetiming valve 340 retains the outer piston O in a nonactuated statethrough communicating the passage 127 to an exhaust port 127'. When inthis arrangement a manual shifting from N- to R position is performed,the oil pressure is first supplied via the passage 110, the 2-3 shiftvalve 230, the passage 121 and the flow control valve 305 to the innerpiston I, then the oil pressure is supplied to the oil chamber 344 ofthe timing valve 340 via the passage 122. The spool 347 of the timingvalve 340 is thus urged to move to the left in response to the pressurerise, whereby passages 126 and 127 are communicated with each other toactuate the outer piston O of the clutch C₂.

Now, in case where the N-D shifting is manually operated, in the firstspeed, a spool 222 in the 1-2 shift valve 220 is placed in the rightposition, releasing the oil pressure from oil passages 116 and 117communicated to the brakes B₁ and B₂ and releasing the oil pressure froman oil passage 118 communicated to the brake B₃ so that the brakes B₁,B₂ and B₃ are released.

In the first speed, the timing control valve 340 receives the linepressure in its right oil chamber 341 which is provided through an oilpassage 108 as a branch of the oil passage 105, the line pressurecausing the spring 345 backing the spool 347 to be compressed to movethe spool 347 to the left position.

When the car reaches a preset speed, the output signal from the computercircuit disenergizes the solenoid valve 330, moving the spool 222 in the1-2 shift valve 220 to the left position to allow the line pressuresupplied from oil passages 105 and 117 to gradually engage the brake B₂through the flow control valve 310 and the accumulator valve 280, theline pressure being also introduced through the oil passage 128 into theleft oil chamber 346 of the timing control valve 340. The sum of theforce of the spring 345 and the gradually increasing oil pressure in theoil chamber 346 reaches a value greater than the line pressure on theland 342, at which time the spool 347 begins to be moved toward theright. After a preset period of time (timing lag) elapses, the spool 347reaches the right position. As the first solenoid valve 320 is beingenergized (see Table 3) to place the spool 232 in the 2-3 shift valve230 in the left position, the oil pressure is introduced into the brakeB₁ through the route of the oil passage 106→2-3 shift valve 230→oilpassage 113→intermediate coast modulator valve 255→oil passage 124→1-2shift valve 220→oil passage 166→timing control valve 340→oil passage125, causing the brake B₁ to be actuated. This causes a shifting to thesecond speed in which the engine brake is capable of working. At thistime, the timing control valve 340 provides a timing control whichpermits the brake B₁ to be actuated after the transmission is shifted tothe second speed and synchronized thereto due to engagement of the brakeB₂.

Shifting to the third speed is accomplished in the following manner: theoutput provided by the computer circuit in response to a certainthrottle position and vehicle speed disenergizes the solenoid valve 320,moving the spool 232 in the 2-3 shift valve 230 to the right position toallow the oil pressure to be supplied through the oil passages 106 and121 and the flow control valve 305 to the clutch C₂ for effectingengagement, while simultaneously releasing the oil pressure from the oilchamber 223, which causes the spring 221 to lock the spool 222 of the1-2 shift valve 220 in the left position.

In this third speed, the oil chamber 344 in the timing control valve340, which is defined by the land 342 and the land 343 of apredetermined diameter greater than the land 342, receives the oilpressure introduced from the oil passage 122 branched from the oilpassage 121 so that the spool 347 can be moved to the left position,allowing the oil passage 125 to communicate with the drain port 127',thus releasing the oil pressure resulting in releasing the brake B₁.

Shifting to the fourth speed is effected in a manner wherein the outputprovided by the computer circuit as above disenergizes the solenoidvalve 330, causing the spool 242 in the 3-4 shift valve 240 to move tothe right position to allow the oil pressure to be released from the oilpassage 120 with the oil pressure introduced into the oil passage 115,releasing the clutch C₀ and engaging the brake B₀.

The shifting from the fourth to third speed is accomplished in thereverse sequence to that in which the above shifting from the third tofourth speed is done. The downshifting is effected in the sequence inwhich energizing the solenoid valve 330 causes the spool 242 in the 3-4shift valve 240 to be moved to the right position, allowing the oilpressure to be released from the oil passage 115 while allowing the oilpressure to be introduced into the oil passage 120 so that the brake B₀is released and the clutch C₀ is engaged.

The following gives a description of the shifting from the third tosecond speed and how the operation of the timing control valve accordingto the invention is operated in connection with the shifting.

Energizing the solenoid valve 320 causes the spool 232 in the 2-3 shiftvalve 230 to be moved to the left position, allowing the oil pressure tobe released from the oil passage 121 while allowing the operating oilpressure PC₂ through the oil passage 122 in the inner piston I for theclutch C₂ to begin gradually to be reduced. Before the downshifting fromthe third to second speed is commenced, an external force expressed inthe inequality (1) below is exerted on the spool 347 in the timingcontrol valve 340, placing the spool 347 in the left position.

    PB.sub.2 ×A.sub.3 +Fs≦PL×A.sub.1 +PC.sub.2 (A.sub.2 -A.sub.1)                                                 (1)

Then, the operating oil pressure PC₂ is gradually decreasing and theexternal force on the spol 347 reduces to such an extent as expressed inthe inequal relation (2) hereinbelow, which causes the spool 347 to moveto the right position, allowing the oil passages 116 and 125 tocommunicate with each other and thus allowng the brake B₁ to be engaged.The downshifting 3 to 2 then comes to completion.

    PB.sub.2 ×A.sub.3 +Fs>PL×A.sub.1 +PC.sub.2 (A.sub.2 -A.sub.1) (2)

where A₁, A₂, A₃, Fs and PB₂ remain constant.

Therefore, the value of PC₂ required to cause the spool 347 to move tothe right position and thus the brake B₁ to operate is determined fromthe equation (3). If the pressure-applicable cross-sections of the lands(piston portions) in the valve is determined so that A₂ -A₁ >0 and A₃-A₁ <0 are complied, PB₂ becomes equal to PL on the 3-2 downshifting.

    PC.sub.2 =(PB.sub.2 A.sub.3 -PLA.sub.1)/(A.sub.2 -A.sub.1)+Fs/(A.sub.2 -A.sub.1)                                                 (3)

As a result, the value PC₂ decreases in inverse proportion to theincrease in the line pressure PL which occurs as the throttle openingdegree increases. FIG. 5 presents the relationship between the linepressure PL and the operating oil pressure PC₂, which makes the equation(3) valid when PL varies from 3.92 kg/cm² to 8.39 kg/cm² according tochanges in the throttle opening degree with A₁ =0.916 cm², A₂ =1.4103cm² and A₃ =0.7854 cm² given. As the operating oil pressure PC₂necessary to cause the brake B₁ to be engaged decreases inversely as thethrottle opening degree increases, the timing of engaging the brake B₁is delayed relatively to the increasing throttle opening degree, so thatthe timing lag between releasing the clutch C₂ and engaging the brake B₁can be sufficiently prolonged (i.e. enhanced) relatively to theincreasing throttle opening degree.

With the manual valve 210 at the position 3, the shiftings to the first,second and third speeds are effected in the same manner as in the Dposition as earlier described, but the shifting to a fourth speed doesnot take place because a line pressure, which is introduced in the rightchamber 243 of the 3-4 shift valve 240 from the oil passages 106 and114, causes the spool 242 to be locked in the left position. If themanual valve 210 is manually operated to shift from D to 3 positionwhile the car is running in the fourth speed (shift range) with thevalve 210 at D position, the downshifting to the third speed takes placeimmediately.

If the manual valve 210 is placed at 2 position, a shifting to the firstspeed takes place in the same manner as at D position. In the secondspeed, the oil pressure from the oil passages 106 and 116 causes thebrake B₁ to be engaged so as to make the engine brake work effectively.If manual shifting to 2 position takes place while the car is cruisingin the third speed, the computer circuit responds to a prescribedvehicle-speed with a certain value, providing an output which energizesthe solenoid valve 320 to effect a downshifting from 3 to 2.

When the manual valve 210 is shifted to L position, the oil pressure isintroduced into the oil passage 109, producing a line pressure in theright oil chamber 233 of the 2-3 shift valve 230 to cause the spool 232to be locked in the left position and thus immediately to result in adownshift from 3 to 2. The 2-1 downshifting then takes place in whichthe output provided by the computer circuit in response to a prescribed,lower vehicle speed disenergizes the solenoid valve 330. At the sametime, the oil pressure in the oil passage 109 is introduced through theoil passage 107, the low coast modulator valve 250, and the oil passages123 and 118 into the brake B₃ for engagement.

The following gives a description of the electronics circuit (computer)shown in FIG. 6 which responds to changes in the vehicle runningconditions for controlling the operation of the first and secondsolenoid valves 320 and 330 as defined in Table 3.

The electronics circuit comprises a power supply circuit 420, and acomputer circuit 400 which includes vehicle-speed and throttle openingdegree sensing means as an input element and a drive output element forthe solenoid valves 320 and 330, including other intermediate circuitelements to later be described in detail. A switch 421 in the powersupply circuit 420 is connected to an external battery (not shown) andis also connected to a position switch 422 on the manual lever 210. Theposition switch 422 is selectively connected through a lead wire 520 toD, 3, 2, L positioning means, and through a lead wire 521 to a powersupply (constant voltage supply) 423 which provides constant voltagethrough a lead wire 523 to the circuit elements in the computer circuit400.

The computer circuit arrangement comprises vehicle-speed sensor 401,reshaper with amplifier incorporated 402, D-A (digital-analog) converter403, throttle-position switch 413, throttle opening degree voltagegenerator 414, 1-2 shift discriminator 404, 2-3 shift discriminator 406,3-4 shift discriminator 408, hysteresis circuits 405, 407, 409, valvecontrol circuit 410 for the solenoid valve 320, valve control circuit412 for the solenoid valve 330, N-R shift signal generator 415, timer411, amplifiers 416, 417, and solenoid valves 320, 330.

The vehicle-speed sensor 401 provides a sine curve signal in response tothe vehicle speed, and the signal is fed to the reshaper 402 whichreshapes it into a positive rectangular signal, which is furthersupplied to the D-A converter 403. The D-A converter 403 provides a D.C.voltage signal whose magnitude depends upon the vehicle speed. Thethrottle opening degree sensing switch (throttle position switch) 413detects engine loads, and includes a variable resistance means whichvaries with the throttle opening degrees. This switch 413 provides anoutput signal indicative of a throttle opening degree and the signal isdelivered to the throttle opening degree voltage generator 414 whichfurther supplies a corresponding D.C. voltage. This voltage is appliedto the 1-2 shift discriminator 404, 2-3 shift discriminator 406, and 3-4shift discriminator 408, respectively. Each of the discriminatorsincludes a differential amplifier, for example, which compares avehicle-speed voltage signal and a throttle opening degree voltagesignal to determine any one of the 102 shift, 2-3 shift and 3-4 shift.The hysteresis circuits 405, 407 and 409 provide the respectivedownshifting conditions corresponding to the 2-1 shift, 3-2 shift and4-3 shift, and permit the respective downshifting to be effected at aslightly lower vehicle speed points than at the respective upshiftingvehicle speed points, thereby preventing buzzing and chattering at gearshifting speed regions.

The opening control circuit 410 for solenoid valve 320 provides outputsignal "0" (OFF) or output signal "1" (ON) depending on the output ofthe 2-3 shift discriminator 406. The output of the circuit 410, which isamplified by the amplifier 416, controls the solenoid valve 320 foropening or closing depending on the output level received. The openingcontrol circuit 412 for the solenoid valve 330 delivers an output signal"0" or an output signal "1" depending on the output of the 1-2 shiftdiscriminator 404, the output of the 3-4 shift discriminator 408, andthe output of the N-R shift signal generator 415 which is fed throughthe timer 411 to the circuit 412. The output of the circuit 412 isamplified by the amplifier 417 for controlling the solenoid valve 330for opening or closing.

The timing control valve which has been described with reference to thepreferred embodiments of the present invention has its operationcontrolled by the line pressure exerted on the spool therein and bytaking advantage of the increase in the line pressure that takes placeas the throttle position increases. It is therefore advantageouslypossible to increase the timing lag between releasing of the clutch C₂and engaging the brake B₂ in relation to the increase in the throttleopening degree, and thus permit a smooth downshifting.

Although the invention has been described with reference to the severalpreferred embodiments thereof, it should be understood that variouschanges and modifications may be made within the scope and spirit of theinvention.

What is claimed is:
 1. An automatic transmission control apparatus ofthe type in which a shifting to one shift range is provided essentiallyby engaging a first friction clutch (C₁) and a friction brake (B₁) foreffectuating engine braking or for aiding in the operation of a one-wayclutch, said automatic transmission control apparatus including a timingcontrol valve (340) functioning in a manner such that a shifting from ahigher speed shift range to said one shift range is effectuated bycausing said friction brake (B₁) to be engaged after releasing a secondfriction clutch (C₂) which has been in engagement at said higher speedshift range and causing said one-way clutch, if any, to be engaged, saidtiming control valve (340) comprising:(a) a spool (347); (b) a spring(345) biasing said spool (347) in a first direction; (c) a first chamber(341) having a pressure-applicable area A₁ to which hydraulic linepressure (PL) may be supplied to bias said spool (347) in the directioncounteracting the biasing force of said spring (345); (d) a secondchamber (344) having a pressure-applicable area A₂ to which hydraulicpressure (PC₂) from said second friction clutch (C₂) may be supplied tobias said spool (347) in the direction counteracting the biasing forceof said spring (345); (e) a third chamber (348) for controlling supplyand release of hydraulic pressure for said friction brake (B₁); (f) afirst passage (108) communicating hydraulic line pressure (PL) which isa function of engine speed to said first chamber (341); (g) a secondpassage (122) communicating hydraulic pressure (PC₂) from a hydraulicservo of said second friction clutch (C₂) to said second chamber (344);and (h) a third passage (116) communicating hydraulic pressure to saidthird chamber (348) when said spring (345) is not compressed; whereby,when it is desired to shift from a higher speed range to said one shiftrange: (i) said spool (347) is initially in a first position in whichsaid spring (345) is compressed by hydraulic line pressure (PL) in saidfirst chamber (341) and hydraulic pressure (PC₂) in said second chamber(344) and in which said third passage (116) is blocked; (j) release ofhydraulic pressure from said hydraulic servo of said second frictionclutch (C₂) allows the hydraulic pressure (PC₂) in said second chamber(344) to begin gradually reducing; and (k) when the hydraulic pressure(PC₂) in said second chamber (344) has reduced sufficiently so that thebiasing force of said spring (345) exceeds the combined force exerted onsaid spool (347) by the hydraulic pressure in said first (341) andsecond (344) chambers, said spool (347) moves to a second position inwhich said third passage (116) communicates with said friction brake(B₁), the point at which the movement of said spool (347) occurs being afunction of the pressure in said first chamber (341) and thus of enginespeed;
 2. An automatic transmission control apparatus as recited inclaim 1 and further comprising a fourth passage (125) communicating saidthird chamber (348) to said friction brake (B₁).
 3. An automatictransmission control apparatus as recited in claim 1 and furthercomprising a drain port (127') which is in communication with said thirdchamber (348) when said spool (347) is in its first position.
 4. Anautomatic transmission control apparatus as recited in claim 1 whereinsaid third chamber (348) has a pressure-applicable area of zero at leastsubstantially.
 5. An automatic transmission control apparatus as recitedin claim 1 and further comprising a solenoid valve (320) energization ofwhich allows hydraulic pressure to be released from said second frictionclutch (C₂), thereby allowing the hydraulic pressure (PC₂) in saidsecond chamber (344) to begin gradually reducing.
 6. An automatictransmission control apparatus as recited in claim 1 wherein said oneshift range is the second speed shift range.
 7. An automatictransmission control apparatus as recited in claim 1 wherein thepressure-applicable area A₂ is greater than the pressure-applicable areaA₁.
 8. An automatic transmission control apparatus of the type in whicha shifting to one shift range is provided essentially by engaging afirst friction clutch (C₁) and a friction brake (B₁) for effectuatingengine braking or for aiding in the operation of a one-way clutch, saidautomatic transmission control apparatus including a timing controlvalve (340) functioning in a manner such that shifting from a higherspeed shift range to said one shift range is effectuated by causing saidfriction brake (B₁) to be engaged after releasing a second frictionclutch (C₂) which has been in engagement at said higher speed shiftrange and causing said one-way clutch, if any, to be engaged, saidtiming control valve (340) comprising:(a) a spool (347) having a firstposition and a second position; (b) a spring (345) biasing said spool(347) towards its second position; (c) a first chamber (341) having apressure-applicable area (A₁) to which hydraulic pressure (PL) may besupplied to bias said spool (347) towards its first position; (d) asecond chamber (344) having a pressure-applicable area (A₂) to whichhydraulic pressure (PC₂) may be supplied to bias said spool (347)towards its first position; (e) a third chamber (348) for controllingsupply and release of hydraulic pressure for said friction brake (B₁);(f) a first passage (108) communicating hydraulic pressure (PL) which isa function of engine speed to said first chamber (341); (g) a secondpassage (122) communicating hydraulic pressure (PC₂) from a hydraulicservo of said second friction clutch (C₂) to said second chamber (344);(h) a third passage (116) communicating hydraulic pressure to said thirdchamber (348) when said spool (347) is in its second position; and (i) adrain port (127') which is in communication with said third chamber(348) when said spool (347) is in its first position; whereby, when itis desired to shift from a higher speed range to said one shift range:(j) said spool (347) is initially in its first position, said spring(345) being compressed by hydraulic pressure (PC₂) in said secondchamber (344) and hydraulic pressure (PL) in said first chamber (341),and said third passage (116) being blocked; (k) release of hydraulicpressure from said hydraulic servo of said second friction clutch (C₂)allows the hydraulic pressure (PC₂) in said second chamber (344) tobegin gradually reducing; (l) the timing for movement of said spool(344) from its first position to its second position after said secondfriction clutch (C₂) has been released is increased in response toincreasing engine speed; and (m) when the hydraulic pressure (PC₂) insaid second chamber (344) has reduced sufficiently, said spool (347)moves to its second position, in which said third passage (116)communicates with said friction brake (B₁), the point at which themovement of said spool (347) occurs being a function of the pressure insaid first chamber (341) and thus of engine speed.
 9. An automatictransmission control apparatus as recited in claim 8 wherein thepressure-applicable area A₂ is greater than the pressure-applicable areaA₁.
 10. An automatic transmission control apparatus as recited in claim8 and further comprising a fourth passage (125) communicating said thirdchamber (348) to said friction brake (B₁).
 11. An automatic transmissioncontrol apparatus as recited in claim 8 wherein said chamber (348) has apressure-applicable area of at least substantially zero.
 12. Anautomatic transmission control apparatus as recited in claim 8 andfurther comprising a solenoid valve (320) energization of which allowshydraulic pressure to be released from said second friction clutch (C₂),thereby allowing the hydraulic pressure (PC₂) in said second chamber(344) to begin gradually reducing.
 13. An automatic transmission controlapparatus as recited in claim 8 wherein said one shift range is thesecond speed shift range.
 14. An automatic transmission controlapparatus of the type in which a shifting to one shift range is providedessentially by engaging a first friction clutch (C₁) and a frictionbrake (B₁) for effectuating engine braking or for aiding in theoperation of a one-way clutch, said automatic transmission controlapparatus including a timing control valve (340) functioning-in a mannersuch that a shifting from a higher speed shift range to said one shiftrange is effectuated by causing said friction brake (B₁) to be engagedafter releasing a second friction clutch (C₂) which has been inengagement at said higher speed shift range and causing said one-wayclutch, if any, to be engaged, said timing control valve (340)comprising:(a) a spool (347) having a first position and a secondposition; (b) a spring (345) biasing said spool (347) towards its secondposition; (c) a first chamber (341) having a pressure-applicable area A₁to which hydraulic pressure (PL) may be supplied to bias said spool(347) towards its first position; (d) a second chamber (344) having apressure-applicable area A₂ to which hydraulic pressure (PC₂) may besupplied to bias said spool (347) towards its first position; (e) athird chamber (348) for controlling supply and release of hydraulicpressure for said friction brake (B₁); (f) a first passage (108)communicating hydraulic pressure (PL) which is a function of enginespeed to said first chamber (341); (g) a second passage (122)communicating hydraulic pressure (PC₂) from a hydraulic servo of saidsecond friction clutch (C₂) to said second chamber (344); and (h) athird passage (116) communicating hydraulic pressure from anintermediate coast modulation valve (225) to said third chamber (348)when said spool (347) is in its second position, whereby, when it isdesired to shift from a higher speed range to said one shift range: (i)said spool (347) is initially in its first position, said spring (345)being compressed by hydraulic pressure (PC₂) in said second chamber(344) and hydraulic pressure (PL) in said first chamber (341), and saidthird passage (116) being blocked; (j) release of hydraulic pressurefrom said hydraulic servo of said second friction clutch (C₂) allows thehydraulic pressure (PC₂) in said second chamber (344) to begin graduallyreducing; (k) the timing for movement of said spool (344) from its firstposition to its second position after said second friction clutch (C₂)has been released is increased in response to increase in engine speed;and (l) when the hydraulic pressure (PC₂) in said second chamber (344)has reduced sufficiently, said spool (347) moves to its second position,in which said third passage (116) communicates with said friction brake(B₁), the point at which the movement of said spool (347) occurs being afunction of the pressure in said first chamber (341) and thus of enginespeed.
 15. An automatic transmission control apparatus as recited inclaim 14, wherein the pressure-applicable area A₂ is greater than thepressure-applicable area A₁.
 16. An automatic transmission controlapparatus as recited in claim 14 and further comprising a fourth passage(125) communicating said third chamber (348) to said friction brake(B₁).
 17. An automatic transmission control apparatus as recited inclaim 14 and further comprising a drain port (127') which is incommunication with said third chamber (348) when said spool (347) is inits first position.
 18. An automatic transmission control apparatus asrecited in claim 14, wherein said third chamber (348) has apressure-applicable area of at least substantially zero.
 19. Anautomatic transmission control apparatus as recited in claim 14 andfurther comprising a solenoid valve (320) energization of which allowshydraulic pressure to be released from said second friction clutch (C₂),thereby allowing the hydraulic pressure (PC₂) in said second chamber(344) to begin gradually reducing.
 20. An automatic transmission controlapparatus as recited in claim 14, wherein said one shift range is thesecond speed shift range.